Commit message: patch 8.2.5151: reading beyond the end of the line with lisp indenting

Problem:    Reading beyond the end of the line with lisp indenting.
Solution:   Avoid going over the NUL at the end of the line.
CVE: CVE-2022-2183
CWE: CWE-125
Vulnerability description: Out-of-bounds Read in GitHub repository vim/vim prior to 8.2.

Project: vim
File: indent.c

get_lisp_indent(void)
{
    pos_T	*pos, realpos, paren;
    int		amount;
    char_u	*that;
    colnr_T	col;
    colnr_T	firsttry;
    int		parencount, quotecount;
    int		vi_lisp;

    // Set vi_lisp to use the vi-compatible method
    vi_lisp = (vim_strchr(p_cpo, CPO_LISP) != NULL);

    realpos = curwin->w_cursor;
    curwin->w_cursor.col = 0;

    if ((pos = findmatch(NULL, '(')) == NULL)
	pos = findmatch(NULL, '[');
    else
    {
	paren = *pos;
	pos = findmatch(NULL, '[');
	if (pos == NULL || LT_POSP(pos, &paren))
	    pos = &paren;
    }
    if (pos != NULL)
    {
	// Extra trick: Take the indent of the first previous non-white
	// line that is at the same () level.
	amount = -1;
	parencount = 0;

	while (--curwin->w_cursor.lnum >= pos->lnum)
	{
	    if (linewhite(curwin->w_cursor.lnum))
		continue;
	    for (that = ml_get_curline(); *that != NUL; ++that)
	    {
		if (*that == ';')
		{
		    while (*(that + 1) != NUL)
			++that;
		    continue;
		}
		if (*that == '\\')
		{
		    if (*(that + 1) != NUL)
			++that;
		    continue;
		}
		if (*that == '"' && *(that + 1) != NUL)
		{
		    while (*++that && *that != '"')
		    {
			// skipping escaped characters in the string
			if (*that == '\\')
			{
			    if (*++that == NUL)
				break;
			    if (that[1] == NUL)
			    {
				++that;
				break;
			    }
			}
		    }
		    if (*that == NUL)
			break;
		}
		if (*that == '(' || *that == '[')
		    ++parencount;
		else if (*that == ')' || *that == ']')
		    --parencount;
	    }
	    if (parencount == 0)
	    {
		amount = get_indent();
		break;
	    }
	}

	if (amount == -1)
	{
	    curwin->w_cursor.lnum = pos->lnum;
	    curwin->w_cursor.col = pos->col;
	    col = pos->col;

	    that = ml_get_curline();

	    if (vi_lisp && get_indent() == 0)
		amount = 2;
	    else
	    {
		char_u *line = that;

		amount = 0;
		while (*that && col)
		{
		    amount += lbr_chartabsize_adv(line, &that, (colnr_T)amount);
		    col--;
		}

		// Some keywords require "body" indenting rules (the
		// non-standard-lisp ones are Scheme special forms):
		//
		// (let ((a 1))    instead    (let ((a 1))
		//   (...))	      of	   (...))

		if (!vi_lisp && (*that == '(' || *that == '[')
						      && lisp_match(that + 1))
		    amount += 2;
		else
		{
		    that++;
		    amount++;
		    firsttry = amount;

		    while (VIM_ISWHITE(*that))
		    {
			amount += lbr_chartabsize(line, that, (colnr_T)amount);
			++that;
		    }

		    if (*that && *that != ';') // not a comment line
		    {
			// test *that != '(' to accommodate first let/do
			// argument if it is more than one line
			if (!vi_lisp && *that != '(' && *that != '[')
			    firsttry++;

			parencount = 0;
			quotecount = 0;

			if (vi_lisp
				|| (*that != '"'
				    && *that != '\''
				    && *that != '#'
				    && (*that < '0' || *that > '9')))
			{
			    while (*that
				    && (!VIM_ISWHITE(*that)
					|| quotecount
					|| parencount)
				    && (!((*that == '(' || *that == '[')
					    && !quotecount
					    && !parencount
					    && vi_lisp)))
			    {
				if (*that == '"')
				    quotecount = !quotecount;
				if ((*that == '(' || *that == '[')
							       && !quotecount)
				    ++parencount;
				if ((*that == ')' || *that == ']')
							       && !quotecount)
				    --parencount;
				if (*that == '\\' && *(that+1) != NUL)
				    amount += lbr_chartabsize_adv(
						line, &that, (colnr_T)amount);
				amount += lbr_chartabsize_adv(
						line, &that, (colnr_T)amount);
			    }
			}
			while (VIM_ISWHITE(*that))
			{
			    amount += lbr_chartabsize(
						 line, that, (colnr_T)amount);
			    that++;
			}
			if (!*that || *that == ';')
			    amount = firsttry;
		    }
		}
	    }
	}
    }
    else
	amount = 0;	// no matching '(' or '[' found, use zero indent

    curwin->w_cursor = realpos;

    return amount;
}